This invention relates to cutting tools and, more particularly, to an improved convertible swivel knife.
There have been previously devised many types of hand-held cutting tools for use by craftsmen such as draftsman, artists, photographers, etc. The majority of such cutting tools employ a small blade that is rigidly mounted at the end of a housing. This type of knife is satisfactory for use in certain applications but has been found deficient in applications where it is necessary to cut curved shapes. The disadvantage stems from the need to continually twirl the fingers or lift the hand to impart the required curved impetus to the cutting blade.
Responsive to the described need there has been developed a type of cutting tool known as a "swivel knife" which employs a blade that is free to rotate about the axis of the cutting tool. Thus, as the craftsman's hand is moved around the curve, the blade will orient itself in the direction required for continued motion and the amount of twirling of the fingers or lifting of the hand that was previously necessary is substantially diminished. In order to make this type of cutting tool more versatile and equally suitable for applications where a rigid blade would be more desirable, provision is often made for rendering the blade-holding mechanism of such knives stationary with respect to the knife housing; i.e., preventing rotation of the blade with respect to the housing. Generally, the blade is attached to the central shaft which is rotatable within the knife housing and the usual technique is to provide a small bore through the shaft in which a pin can be inserted. The bore is accessible by removal of a cover at the top of the cutting instrument. Therefore, when it is desired to convert the action of the knife from "swivel" to "non-swivel", or vice versa, it is necessary to remove the cap, either insert or remove the pin, and then replace the cover. This technique is somewhat inconvenient in that it requires the manipulation and storage of a pin element that is quite small.
Improved techniques for convertible swivel knives have been devised with the mechanisms employed requiring, for example, threaded elements which must be turned by the user. Such techniques tend to increase the manufacturing cost of the knives by requiring precision threaded parts and/or an increase in the number of parts needed to perform the required function. Examples of these techniques are shown in U.S. Pat. Nos. 2,569,286 and 3,831,276.
A further problem with prior art swivel knives relates to the provision for bearings which allow smooth relative rotation as between the blade-holding shaft and its housing. If no restrictions on size or expense were necessary, precision bearings could be readily provided. However, a convertible swivel knife is a hand-held tool which must necessarily be limited in length and diameter and have reasonably good weight distribution and balance. Accordingly, any bearing system provided should be compact, easy to assemble, and have a minimum number of parts, while still performing an optimum function.
It is an object of this invention to provide an improved swivel knife which overcomes the disadvantages of presently available cutting tools.